Disc drives are digital data storage devices that enable users of computer systems to store and retrieve large amounts of data in a fast and efficient manner. Disc drives of the present generation have data storage capacities in excess of tens of gigabytes (GB) and can transfer data at sustained rates of several megabytes (MB) per second.
A typical disc drive includes a plurality of magnetic recording discs which are mounted to a rotating hub of a spindle motor for rotation at a constant, high speed. An array of read/write heads are disposed on adjacent surfaces of the discs to transfer data between the discs and a host computer. The heads are radially positioned over the discs by a rotary actuator and a closed loop, digital servo system, and are caused to fly proximate the surfaces of the discs upon air bearings established by air currents set up by the high speed rotation of the discs.
A plurality of nominally concentric tracks are defined on each disc surface. A preamplifier and driver circuit generates write currents that are used by the head to selectively magnetize the tracks during a data write operation and amplifies read signals detected by the head during a data read operation. A read/write channel and interface circuit are operably connected to the preamp and driver circuit to transfer the data between the discs and the host computer.
Disc drives may be used in a stand-alone fashion, such as in a typical personal computer (PC) configuration where a single disc drive is utilized as the primary data storage peripheral. Alternatively, in applications requiring great amounts of data storage capacity or high input/output (I/O) bandwidth, a plurality of drives can be arranged into a multi-drive array, such as a RAID (“Redundant Array of Inexpensive Discs”; also “Redundant Array of Independent Discs”).
As is known, a disc drive requires maximum power during a spin-up phase of operation where the spindle motor of the disc drive is brought up to operating speed. In many cases, a disc drive may draw up to double its steady state operational power during spin-up. As such, when a number of disc drives are arranged in an array, precautions must be taken so that the capability of the power supply of the disc drive array is not exceeded during spin-up of the disc drives in the array.
One way to ensure that the capability of the power supply of a disc drive array is not exceeded is to use a large capacity power supply that provides enough power to handle the simultaneous spin-up of all of the disc drives in the array. However, such large capacity power supplies add significantly to the overall cost of the disc drive array. In addition to the high cost of the large capacity power supply, there are also the related costs of extra cooling and space requirements in the disc drive array for the large capacity power supply, as well as greater overall energy use of a disc drive array so equipped.
Another way to ensure that the capability of the power supply of a disc drive array is not exceeded is to stagger the spin-up of the disc drives in the array. Typical SCSI disc drives provide a number of mechanisms to delay the spin-up of the disc drives with respect to each other. In a typical SCSI disc drive, a default “Auto Start” state causes the disc drive to spin-up automatically when power is supplied to the disc drive. To delay this Auto Start feature, and thus to delay the start of spin-up, some SCSI disc drives provide a “Disable Auto Start” jumper. When the “Disable Auto Start” jumper is set, spin-up will not occur until a start command is received by the disc drive over the SCSI bus. As such, in SCSI disc drive arrays utilizing disc drives employing the Disable Auto Start feature, the sequencing of the spin-up of each disc drive in the array may be controlled by selectively sending start commands from a host computer or array controller to the disc drives in the array.
Another mechanism that is used in SCSI disc drives to delay the spin-up time is the “Delay Auto Start” jumper. When the “Delay Auto Start” jumper is set, the spin-up of the SCSI disc drive occurs automatically a predetermined delay time after power is applied to the drive. This predetermined delay time may either be a fixed predetermined delay time or, alternatively, may be a fixed number that is multiplied by the SCSI device ID number of the disc drive to produce a desired delay time. By carefully selecting the fixed number for each disc drive of a SCSI disc drive array, the spin-up time of each disc drive in the array may be delayed or sequenced in a desired manner.
In contrast to SCSI disc drives, spin-up in typical parallel-ATA disc drives and typical serial-ATA disc drives is not controlled by commands received from a host computer or array controller. In typical parallel-ATA disc drives a scheme may be employed wherein when two parallel-ATA disc drives are used on the same ATA channel as master and slave, the spin-up of the slave drive is delayed by several seconds from the spin-up time of the master drive. Unfortunately, as a typical parallel-ATA channel may only accommodate a single pair of master/slave devices, the spin-up of only one disc drive per parallel-ATA channel may be delayed in this manner. Present serial-ATA disc drives do not include any mechanisms for staggering or sequencing the spin-up of a plurality of disc drives. In particular, there is currently no master-slave relationship in the point-to-point topology of serial-ATA interfaces.
SCSI disc drives have typically been preferred over ATA disc drives in arrays having a large number of disc drives. Part of the reason for this preference relates to the better spin-up time control that they provide. Unfortunately, SCSI disc drives are typically much more expensive that ATA disc drives. As such, there is a need for systems and/or methods that provided a greater control of spin-up times of ATA disc drives, so that inexpensive arrays of ATA disc drives may be more effectively used in multi-drive arrays.